1. Field of the Invention
This invention relates generally to a high dielectric constant capacitor, and, more particularly, to a high dielectric constant capacitor which utilizes a multilayer dielectric film having improved dielectric properties. This invention also relates to a method for making such a high dielectric constant capacitor. It is presently contemplated that this invention may have particular utility in very large scale integrated circuits (VLSIs), such as semiconductor memory devices, e.g. RAMs.
2. Description of the Prior Art
VLSIs, such as semiconductor memory devices having a large memory capacity, utilize miniature capacitors which are required to have a high capacitance, despite their small area. In order to achieve the required high capacitance, dielectric films having a high dielectric constant, such as tantalum oxide (Ta.sub.2 O.sub.5) films, have been used in such miniature capacitors.
Generally, such tantalum oxide dielectric films are formed by means of a low pressure chemical vapor deposition (LPCVD) technique. However, tantalum oxide dielectric films formed in such a manner exhibit oxygen deficiency, which results in capacitor performance problems, such as unacceptably high leakage current and unacceptably low dielectric breakdown voltage.
One approach which has been proposed to overcome the above-mentioned drawbacks with tantalum oxide dielectric films, is described in U.S. Pat. No. 4,734,340, issued to Saito et al., and, in an article entitled "Electrical Properties of Thin Ta.sub.2 O.sub.5 Films Grown By Chemical Vapor Deposition", @ pp. 680-683 of the IEDM Technical Digest (1986), by Saito et al. In accordance with this approach, the dielectric film is made of a mixture of tantalum oxide and titanium oxide. However, this approach only partially solves the oxygen deficiency problem, because the ratio of Ti to Ta is limited to a range of from 0.1 to 4 atomic
Thus, there still exists a need for a high dielectric constant capacitor which more fully overcomes the above-described drawbacks of presently available high dielectric constant capacitors. The present invention fulfills this need, while also providing a miniature capacitor which has a higher dielectric constant than the presently available miniature capacitors.